Screen grate for ball mills



Aug. 2 1927.

- W. CURRIE SCREEN GRATE' FOR BALL MILLS Original Filed MaM'ZO, 1924 2 Sheets-Sheet E R R F C M m L m 0 2 ug w. CURRIE SCREEN GRATE FOR BALL MILLS 2 Sheets-Sheet 2 Original Filed May 20, 1924 -W\LL\AM C name Patented Aug. 2, 1927.

UNITED STATES PATENT oFFicE.

WILLIAM CURRIE, or CARTERET, NEW JERSEY, ASSIGNOR To CHROME STEEL Worms;

' or CARTERET, NEW JERSEY, A CORPORATION 0E NEW JERSEY.

SCREEN GRATE FOR BALL MILLS.

Application riled May 20, 1924, Serial This invention relates to ball mills and has special reference to a ball mill grate.

In the construction of ball millsof the horizontal cylinder type the body of the mill is provided at one end with an inlet opening for the material to be crushed and at its other end with an outlet adjacent to which is a screen for the purpose of preventing the passage from the outlet of particles of the substance being crushed which are over a certain desired size. These screens are usually made with parallel bars of metal and are called grates, the bars being tapered in cross-section and arranged side by side so that spaces are provided between such bars of proper width to pass that portion of the material being crushed. which has been sufficiently comminuted. These grates are subject to heavy shocks as well as much wear and may be considered in two general classes in one of which the grate bars are secured side by side by means of bolts passing through suitable lugs and in the other of which the bars are cast as a unit segment of the entire grate. In the first of these methods it is practically impossible to maintain the bars in proper spaced relation and the employmentof bolts is objectionable for this reason. In the second method difiiculty arises from three sources, one of which is the expense of coring the slots between the bars, the second being the difliculty of obtaining a hard casting which is not too highly frangible and the third being the difiiculty of obtaining castings wherein the internal stresses due to the cooling of the molten metal will not distort the grate segment to such an extent that variations exist in the widths of the slots between the bars.

It has been sought to overcome these difficulties by providing bars of rolled metal such as hard steel and casting a frame around them so that the ends are held in the side members of the castings, such side members being tied together at their respective ends by end members. While some of the difficulty has been overcome in this manner the fact that the side members are tied together between ends of the frame produces very objectionable effects since the cooling of the end members from their molten state to normally atmospheric temperature results in very heavy tensile stresses being set up in No. 714,651. Renewed June 25, 1927.

ends connected by castings forming ties'for such ends the castings being separate for each set of ends so that no stresses tending to distort the segmental-e .set up.

With the above and other objects in view the invention consists of I segment which will now be particularly described, specifically claimed, and illustrated in the accompanying drawings wherein:

Figure 1 is a face view of one segment and a portion of a second shown in position in a part of a'ball mill.

Figure 2 is a section on the line 22 of Figure 1.

Figure 3 is an edge view of one of the grate bars separate from the segment.

Figure 4 is a side View of such bar from the pad provided side.

Figure 5 is a View similar to Figure 4 showing one of the bars with the tie castings thereon in section.

Figure 6 is an enlarged detail section through a pair of the bars showing narticularly the spacing pad arrangement.

' Figure 7 is a detail view of one end of a. grate bar and the tie casting in a form somewhat modified to that shown in Figure 5.

In the formation of these bars, a suitable bar of steel is rolled or forged under the hammer, the rolling being preferred, to form bar metal of trapeziodal crossasectiom such bar metal having spaced pads rolled or forged thereon at suitable intervals.

This bar metal is then cut into lengths to provide grate bars 10 having beveled ends 11 provided with locking notches which may either be segmento-cylindrical as at 12 or under cut as at 13. The pads for these bars are shown at 14. These bars are arranged in sets graduating in lengths with the pads of one bar resting against the flat side of an adjacent bar. the ends being positioned in proximal relation to form two sets of ends.

.Each set of bars then has cast 011 each set of its ends a tie bar 15, the metal of which enters the locking dovetail slots as shown at an improved grate Q g g r 1,637,986

16. These tie bars of cast metal are individual tie bars and. not only frictionally grasp the metal of the grate bars but are mechanically held against disengagement therefrom by the locking slots. The tie bars are then suitably machined and each segment thus formed for placing in position in the ball mill and there held by fastening means such as is illustrated in general at 17 the same being a well known means and forming no part of the present invention which relates solely to the construction forming the grate segment-s themselves.

With a grate segment thus formed the space between the shell 18 of the ball mill and the segment may be filled with a suitable filler block 19 Thus this method of construction involving the use of hard forged steel grate bars and tie castings on the ends, the bars and ties being provided with mechanical interlocking elements, enables such segments to be made with economy and eliminates the possibility of distortion of the bars and the detachment of the ties from the bar ends.

What is claimed is r 1. A ball mill grate'segment consisting of a series of forged hard steel grate bars'arranged side by side in spaced relation and having their ends disposedin two sets, and separate cast metal ties eacliembracingone set of ends.

2. A ball mill grate segment consisting of a series of forged hard steel grate bars art ranged side by side in, spaced, relation and having their ends disposed in two sets, each end ofeach bar being-provided with looking slots, and separate metal ties cast in place and each embracing one set of ends andffilling said slots. i Q 3. A ball mill grate segment consisting of a series of forged hard'steel grate bars arranged side by side in spaced relation and having their ends disposed in two sets, each end of each barbeing provided with lock ing dovetail slots, and separate metal ties cast in place and each embracing one'set of ends and filling said slots. In testimony whereof I aflix my signature.

WILLIAM conn n 

